Spread a quarter of the tomato mixture in the slow cooker. Arrange a layer of noodles over the sauce, overlapping them slightly and breaking into pieces to cover as much of the sauce as possible. Spread half of the ricotta-vegetable mixture over the noodles and firmly pat down, then spoon on another quarter of the tomato sauce and add a third of the mozzarella.

Repeat the layering once more, starting with the noodles.

Top with a third layer of noodles. Evenly spread the remaining tomato sauce over the noodles. Finish off with the remaining noodles over the tomato sauce.

Set aside the remaining of the mozzarella in the refrigerator.

Cook

Put the lid on the slow cooker and cook on 'High' for 2 h or 'Low' for 4 h.

Turn off the slow cooker, add the reserved mozzarella on the lasagna, cover and let stand for 10 min to allow the cheese to melt. Serve.